REPRODUCTION OF SOUND TRACK SIGNALS BY VARYING THE DETECTOR THRESHOLD LEVEL AS A FUNCTION OF THE TRANSVERSE SCAN POSITION

摘要

Audio information is recovered from a variable-area optical record, particularly motion picture film variable-area optical soundtracks. A scan signal is obtained by repetitively scanning the optical record substantially transverse to the bias line. The noise reduction effect is enhanced by a threshold detector which is provided with a transversely varying threshold level that varies according to the position of the scan across the width of the soundtrack. A threshold is provided for a bilateral soundtrack, the threshold having a minimum level at the bias line of the soundtrack and increasing progressively with distance from the bias line. Thus, on each scan, the threshold level is high when the scan is at the edge of each soundtrack, falls progressively to a minimum when the scan reaches the bias line, and then increases progressively back to its original high level when the scan is at the other edge of the soundtrack.